


A Night of Morally-Questionable Decision Making

by marguerite_26



Category: Teen Wolf (TV)
Genre: Alternate Universe - Canon Divergence, Brother-Sister Relationships, Derek Hale Has a Big Dick, F/M, Happy Poly, Just the Tip, Loss of Virginity, M/M, Multi, Polygamy, Protective Older Brothers, Sibling Incest, Size Kink, Threesome - F/M/M
Language: English
Status: Completed
Published: 2014-11-11
Updated: 2014-11-11
Packaged: 2018-02-22 17:58:28
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 7,075
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/2516741
Author URL: https://archiveofourown.org/users/marguerite_26/pseuds/marguerite_26
Summary: <blockquote class="userstuff">
              <p>"He's perfect, Derek," Cora says, like she's asking permission. </p><p>Her breath is hot against the back of Stiles' neck while her fingers toy with his belt buckle. Stiles squirms in her hold, confused and self-conscious. They're still in the apartment doorway, talking to her brother. He doesn't have a lot of experience, but he's pretty sure this isn't normal hookup procedure.</p>
            </blockquote>





	A Night of Morally-Questionable Decision Making

**Author's Note:**

  * For [yue_ix](https://archiveofourown.org/users/yue_ix/gifts).



> Thanks to Eleadore and Otta for the advice and beta review.  
> Yue_ix, I sincerely hope you find this to your liking. ;)

It's a Friday night but the bar's not crowded. Beacon Hills doesn't have a population to support a lot of nightlife, and a newer, trendier club opened down the street from this one. The drinks are cheaper here and the line shorter (non-existent) to get in. 

Besides, the bouncer barely glanced at Stiles' fake ID so he knew right then he made the right choice of establishments.

He's a few drinks in with a nice buzz going when a gorgeous brunette sits down on the stool beside him.

"Cora," she says, her hand on his thigh.

"Cool, yeah. This is... good." Stiles swallows, trying to act like girls' hands find their way to his thigh all the time. "Stiles."

Cora's lips are plump and pink, and Stiles' mind wanders to a few fantasies as she licks them. "I've never tried to pick anyone up before," she says and Stiles chokes on a nervous laugh.

Her hand moves up an inch, which should go against what she's saying, but there's nothing really _practiced_ about her. Her cheeks are flushed and Stiles guesses she's about as drunk and as nervous as he is, only less worried about rejection. She has a point too, because she could probably go home with any guy in this place. He's almost tempted to ask, _why me_?

"Wow, I'm so incredibly bad at this." Stiles ducks his head, not able to look at her as he says, "and you are so _incredibly_ hot." He sneaks a peek to gage her reaction and sees a small, pleased grin, like his idiocy is exactly what she's looking for.

The thrum of the music beats in time with the tapping of Cora's finger on the inside of Stiles' thigh. His head pounds as blood rushes through his veins, directed south. Her hand seems to demand attention from every part of his body, like a silent siren being set off with each stroke higher along his inseam. 

Stiles tries to concentrate on Cora's words, on keeping eye contact, on trying to somehow be charming. Sweat trickles down his temple as he bites his lip; it's all he can do to keep his knee from bouncing. He focuses on not flailing out of his seat or coming in his pants.

"What?" Stiles asks, once he realizes from Cora's face he's missed something important.

"--dance," is all he hears over the music. Cora has already turned away from him and is pulling him off the stool as she walks towards the dance floor.

"Okay," Stiles says, though he doubts Cora's listening for a reply.

The dance floor is sparsely filled, only a dozen couples and rowdy group of twenty-something girls braving the scrutiny of the onlookers. Stiles feels like all eyes are on him and Cora as he tries to figure out how close to stand and where to put his hands. It's a disaster. He's seventeen and clueless how to hook up at a bar. 

Cora's not even looking at him anymore. Her eyes are narrowed, looking off somewhere over Stiles' shoulder. 

"Uh," Stiles says. "You really kinda look like you don't want to be here." His eyes dart to the guy leaning against the upper rail separating the sunken dance floor from the rest of the bar. For some reason he's glaring at them fiercely. "We could be elsewhere, like not getting the evil eye from potential serial killers."

Cora rolls her eyes, but not at Stiles. Her attention is focused over to the side, at that same gawker with the particularly angry eyebrows. She shifts their position a bit so they're less on display. "Just… focus on me," she says, leaning in close to his ear, pressing their bodies together and starting to move.

He's never been a talented dancer, but Cora, and the drinks he's already downed, make it easy to forget where they are for a little while. His tension fades and his limbs loosen as he follows her lead, swaying to the music. Her top is slippery beneath his hands and he clutches her hips like he needs to hold tight for the ride. Up close, he can smell her shampoo and he buries his nose into her thick hair to surround himself in it. 

"You smell so good," he whispers in her ear, not even caring how dumb it must sound. He feels her lips, soft against his neck in reply. He pulls away a little and kisses her, feeling confident for the first time in his life that he won't be rejected. 

Stiles' eyes flutter closed as their lips meet, just grazing each other at first. Then Cora's responding, as eager and hungry for this as he is. Her lips are plump, fat and soft beneath his teeth as he nibbles gently, not wanting the kiss to end. This is already the best night of his life.

They find a sweet little rhythm that's mostly rubbing and grinding; he's thankful this isn't some high school dance where Coach is going to break them apart for dry humping instead of dancing. 

Stiles is uncomfortably hard by the time Cora drags him from the dance floor a few songs later. He's trying to be discreet at adjusting himself as they make for an empty booth. There's a light out in the corner they choose and the illusion of privacy is worth the ripped faux-leather bench and sticky table. Taking advantage of the shadows, Cora pounces into a kiss and their teeth clack painfully. They end up giggling against each other's lips and the mood lightens instantly.

They're still laughing and checking for chipped teeth, when a waitress interrupts them and sets down two shots. 

"One for the gentlemen and one for the lady," she says, then turns to Cora and adds, "I was told to tell you Happy Birthday."

Stiles eyes the whipped cream-topped shot in front of him and poses an unspoken question to Cora.

"My brother," she explains. "Such a dork."

"He's, er, here?" Stiles puts a bit of space between them, looking around for a big brute ready to pummel him. An over protective brother might be cliché, but he's always assumed it's cliché for a reason.

"Calm down. He must think you're okay," she says, sliding the shot a bit closer to him. Stiles tentatively picks up the drink, and takes a small sip just as Cora adds, "After all he gave you a blowjob."

He has to clap his hand over his mouth not to spit it out. "What?"

"Odd sense of humor. It runs in the family." Cora grins, the dark shadows from the bad lighting making her look both amused and other worldly. "Maybe he's looking to see if you'll spit or swallow."

"Um." Stiles licks the bit of cream from his lip, unsure how to take all this. "Your _brother_?"

Cora shrugs but looks delighted when Stiles does in fact swallow the shot down in a moment of bravery. The way her face lights up makes him feel like he's passed some test.

Emboldened from winning at whatever game this is, Stiles smirks. "I never turn down a blow job."

"I'll be sure to let him know." 

His laugh is a little shaky, unsure if she's reading him _too_ well. "Okay, what's your shot?" 

"Horny monk." She tips it back and licks her lips chasing the last of the taste. "He thinks he's so funny." She's still talking as her mouth closes in on Stiles'. The kiss is sweet and coffee-flavoured with whatever was in the drink.

The corner's dark enough that Stiles feels he's finally escaped the stares of the dance floor lurkers. He lets Cora press up against him so that he feels the pressure of the wall at his back and her, warm and soft, against his front. He loses himself in the heat of her, in the clever, wet slide of her tongue.

He's buzzing all over. If he was a bit more sober, he might be freaking out about just how perfect a fantasy it is; nothing _this_ good ever happens to him. It doesn't feel real, the alcohol making it dream-like, fuzzy around the edges. The seductive pounding of the music fogs his head until he barely even realizes that Cora's cupping his crotch in public.

Her thumb traces the outline of his painfully hard dick and his hips jerk into her touch. 

"Cora," he whispers, breathless. It's not that he wants to stop but they are sitting beside the path to the bathrooms and there's no hiding what's happening here to someone curious enough to look closely. 

A tiny, romantic part of Stiles' brain -- one that he's never before believed existed -- would like for his first time to be a little more intimate. He's not willing to voice any of that though, because a hand on his dick? He's barely breathing.

Cora takes one last stroke, root to tip, and moves back, declaring, "You're perfect."

"Thanks?" Stiles feels his own wide-eyed stare and just knows he looks stoned or concussed or something.

"Come back to our place?"

"Wow." When Stiles' brain finally catches up with her words, and that she's actually waiting for a response, he rushes out, "Yeah, sure."

She kisses him again, long and deep and full of promises Stiles hopes to hell she's willing to keep.

Next thing he knows, she's leading him through the dark, empty streets of downtown. It's misty and cold, and Stiles is distracted enough trying to get the broken zipper up on his jacket that they've gone a couple blocks before he notices that some guy is following them.

It's only when Cora looks back and rolls her eyes at their stalker that Stiles recognizes the angry eyebrows of the same guy who was staring at them on the dance floor.

The beer and nachos in his stomach churn. "Is that your boyfriend of something? He kinda looks like he wants to kill me." Cora's hot, and God does Stiles ever want whatever she's offering, but he's not about to become some jealous ex's punching bag.

"Nah. That's my brother." Cora stops and the guys stops too. The resemblance is uncanny with their matching bitch faces. "God dammit, Derek! Stop scowling. If you ruin this for me --"

To Stiles' surprise the guy -- _Derek_ \-- raises his hands in defeat. Cora huffs, but looks satisfied as she tugs Stiles' hand to keep moving. He doesn't get a chance to look back again until they're at a doorway to an apartment building.

Derek moves forward to unlock the door and as he steps into the light, Stiles gets a new appreciation for Derek's stubbled jaw line. It's super-hero level strong. The genes in this family are quality.

The door swings open and Derek holds out his arm to let Stiles through first. He's more just _looming_ now, not scowling. Stiles guesses he's okay with his sister hooking up right in front of him, but it feels like he need to say _something_.

"Thanks for the blowjob," spills out of his mouth as he passes, and he waits, wide-eyed for the left hook, positive it's coming. 

Instead, Derek turns red; for a big burly, damn scary-looking guy, he blushes adorably. Stiles finds himself cataloguing that fact like he'll need the info later in this quest.

Cora curls up behind him, chin on Stiles' shoulder. "He swallowed." 

"I saw," Derek says. He's got these pale, grey-green eyes, and the intensity with which they're boring into Stiles does a funny thing to his dick. 

Stiles needs to get a move on, get Cora alone before he accidentally starts flirting with her gorgeous brother, and does something _really_ awkward, like falling to his knees in their front hallway. This is his first hook up -- how is it possible to fuck this up so badly?

As it is, he might have been able to hide his reaction if Cora didn't reach around right then and give him a squeeze. 

"He's perfect, Derek," Cora says, like she's asking permission. 

Her breath is hot against the back of Stiles' neck while her fingers toy with his belt buckle. Stiles squirms in her hold, confused and self-conscious. They're still in the apartment doorway, talking to her brother. He doesn't have a lot of experience, but he's pretty sure this isn't normal hookup procedure.

"Bedroom?" she whispers and Stiles isn't even sure who she's talking to. His eyes go to Derek's for answers. 

Derek's eyebrows rise like he's repeating his sister's question. 

"I don't know the right answer here," Stiles says, voice cracking as Cora's fingers start to work his belt buckle open. He's getting hard so fast it's making him dizzy.

"Yes, is what we're looking for, idiot." Cora gets his zipper down and Stiles squeaks out what might be a tiny 'kay'. She huffs. "Derek, you're making him nervous again."

"Not that nervous." Derek smirks, looking down at Stiles' crotch.

Stiles' stomach goes squirly with the sudden attention on his dick. "Fear boner, okay. It's a thing." 

His face goes hot as Cora leads him to towards the bedroom, his pants still an open V. And it goes hotter still as Derek follows them in, brushing past to take a chair in the corner opposite the bed. 

A noise squeaks from Stiles' throat as he openly stares at Derek _definitely not leaving_.

"You're a virgin right?" Derek says, fidgeting like he's the one that's nervous here. "She was supposed to get a virgin."

"Shut _up_ , Derek." Cora groans, her hands digging into her hair and making it a hot mess. "I swear I'll kick you out. Don't think I won't."

Derek gapes, suddenly defensive as he explains to Stiles, "She should have a virgin for her first time, not some asshole who's slept with dozens of young, vulnerable girls."

Cora clicks her tongue. "Ugh, you are so weird about this."

Yes. Definitely, this is weird, Stiles agrees. He eyes the door, but his peripheral vision catches _skin_ as Cora strips off her top. As much as he really wants to say, 'you are guys are fucked up, bye' when he looks over, Cora's down to nothing but a matching purple bra and panties. It might be the hottest thing he's ever seen. She's toned and curvy, and more confident naked than Stiles ever hopes to be. 

On her left bicep is a tattoo of three connected spirals that Stiles is going to ask about later -- like over breakfast, hopefully. Because Stiles really _is_ a virgin. If his dick can ignore the hot, scary brother who seems to want to witness his first time, Stiles can too. 

Stiles peels off his shirt and jeans, grateful they haven't turned on the main light. The streetlight casts enough of a glow through the thin curtain that he's not self conscious of his pale skin. Maybe they won't even notice his moles. There's no hiding the tent in his boxers though.

The bed's big and looks comfy. Both night stands have lamps, books, alarm clocks, and partially empty water glasses. Stiles tries to ignore what that implies. 

Before he can say something stupid about it, Cora pushes him down onto the feather duvet and climbs onto his lap.

He _loves_ kissing Cora. She's like some sort of expert - Olympic Level. Her lips are soft, and the kiss is wet and demanding. Her tongue teases his just enough to steal a moan from his throat. He could probably kiss her for hours, no complaints. But there's a lot of skin beneath his hands, only bits of lace like speedbumps as his hands stroke down her back, cup her ass and slide back up again. It's not really conducive to keeping his dick from demanding more. 

Cora must be thinking the same because she breaks the kiss to sit up and straddle him. Her bra is off in a blur of purple. 

"Oh, shit. Yeah." Stiles gasps as his hands instinctively reach up to cup the perfect mounds of her bare breasts. A flash of pleasure shoots to his groin as she squirms, her hot cunt rocking against his cock with only the barest strips of cloth separating them. His eyes fall shut as he thrusts upward, fantasizing about slipping inside. 

"You need to eat her out first." Derek's voice is gruff and loud, coming out of nowhere and breaking through Stiles' stupor. 

"What?"

Derek clears his throat and explains, "You need to make her come first."

Cora stills, her nails digging into Stiles' chest in a way that's bordering on painful. "Derek, we're doing fine all on our own."

"You can't _hurt_ her."

Stiles wants to sit up and meet Derek's eye, but Cora keeps him pinned so he just says, "Sure, I mean, I wouldn't--"

"So go down on her. You got a problem with that?"

"Do I? No, of course, whatever she wants, man."

"She wants you to go down on her. It's the only way she can get off without a toy."

Cora gets off him then, standing and turning to her brother, topless. No one seems surprised by this and Stiles is starting to wonder why he bothers being surprised by anything. With her hands on her hips, Cora says, "Could you _be_ more embarrassing?"

"Cora, you agreed to do this my way. Open communication is an important part of sex. You want him to eat you out, you ask him to eat you out."

"Fine!" Her hands fly up in the air and, turning to Stiles, she asks,"You've got an amazing tongue. I want to see what else you can do with it."

"I'm down with going down--" Stiles panics, words falling out of his mouth beyond his control. "If that's what gets you… down." He winces. 

Luckily, Cora smiles, amused instead of annoyed

The remainder of their clothes hit the floor pretty quickly after that. Stiles tries to ignore that he's completely naked while Derek's watching them, still with his leather jacket on.

Stiles lies back. It takes a bit to get comfortable; the pillow's too much height and gets in the way of Cora's knees. He scoots down so his head's about a foot from the headboard and Cora can lean forward to grip the cast-iron bars. 

They figure themselves out eventually and Derek stays quiet through it all. Stiles' erection has hardly flagged in the cool air of the room. It rest on his thigh, waiting for attention. Stiles can be patient.

Cora's majestic above him, all shadowed and radiant as she tosses her head back. Stiles wants to worship her from her smooth, muscled thighs that frame his cheeks to the soft sway of her breasts as she positions her pussy against his mouth. 

Her wet, dark curls tickle his nose and he wants to laugh away his nerves, but he's still too overwhelmed. He forces himself to relax and concentrate on the first taste of her on his tongue. She gasps with the first tentative licks to her clit, and Stiles is fully hard again just like that. 

It's not at all like porn. He can't really see what he's doing, and he's only going by sounds and hoping Cora's not faking anything. With her on top, at least she's controlling where his mouth goes as she tilts her hips and re-directs him when he moves off that swollen nub.

The bed dips at Stiles' knees and he feels the cool tingle of leather. He leans in to welcome the company without thinking too much about his hard, naked cock, bouncing freely for his hook-ups' brother to see.

"Add a finger," Derek says. He's close enough he can speak in barely a whisper.

Stiles hums in agreement, moving enough that he can slip a finger between his chin and her cunt, finding his way slowly up into Cora's wet pussy. She whimpers, grabbing his hair and moving him back in place.

He starts suckling her clit again, sliding his finger in, slow and deep, then drawing it back out. The reaction is instant. Cora rocks against his face, tiny little grunts that sound a thousand times more real, a thousand times hotter than any X-tube vid. 

His face is sloppy wet and his hips lift off the mattress, fucking up into nothing. 

He's keenly aware of the rough friction of jeans against his thigh as Derek moves closer. 

"This is good," Derek whispers, like he's talking to himself, like he doesn't even realise he's voicing his thoughts. "He's making it good for you. You look --- yeah it's better this way."

"He's so smooth, Derek," Cora answers back, raspy and breathless. "His face is smooth and slick. It's so--" She gasps as Stiles' finger moves deeper with each roll of her hips. "So smooth." 

Stiles' mind races with the implication, his dick growing a little harder at the images _stubble burned_ thighs now flooding his mind. He adds another finger, stroking deep inside as she adjusts to him. It's not long before she's riding his face again, faster this time, getting the angle she wants.

Crying out in a choked-off scream, she stills. Her walls squeeze around Stiles' fingers, pulsing around him like they could suck the fingers clean.

Instead, though, his fingers are getting wetter, slick dripping down his wrist. Cora's hips roll softly through the aftershocks, and Stiles pumps his fingers with that same gentleness. He stares up in reverence as she shudders through the last few waves and collapses against the headboard.

It's Derek who moves first, kissing her softly and gentling her onto the other side of the bed. Derek's side of the bed, Stiles adds to himself as he spots a man's watch by the pile of books.

"You okay?" Derek says sweetly, nuzzling against Cora's temple.

Cora nods, flushed and beautiful. Her hair's dark and messy, a few strands sticking to her damp cheeks. She looks up at her brother with a kind of wide-eyed adoration that makes Stiles feel like an unwelcome third wheel in this incestuous threesome. 

They kiss full on the lips, wet and open. He's beginning to realize where Cora got all her practicing in. 

Cora clings to her brother, her body still shaking through the remnants of her orgasm. She claws at his shirt, his arms, finally drifting lower. "You're hard."

Derek exhales a quiet laugh. "Of course I am."

"I'm glad." Cora undoes his belt, his zipper, and reaches inside her brother's jeans. Stiles can't tear his eyes away. "You'd be enjoying yourself more if you were naked with us." She pulls out his cock. 

"Shit," Stiles breathes. It's the biggest cock Stiles has ever seen. Cora's hand is delicate, dwarfed by the massive head her fingers are stroking. As she moves down the shaft she can't even get a proper grip with one hand; her fingers have no hope of making a proper circle. _That thing could do some serious damage_ , is the first though to pop into his brain and everything starts to click in place. 

_I don't want to hurt you,_ triggers in his memory.

"Oh my God," Stiles says. He's so distracted by the revelation he barely notices he's drawn both siblings' attention. "I'm here because my dick's small."

He wipes his face, still a bit sticky from Cora, and looks down. He's never thought of himself as _small_. Average felt like a good, safe word. He'd never drawn attention either way in the locker room, neither big or small enough to get teased; guys were assholes about it.

But average feels less than, at the moment. And he's getting smaller every second he thinks about Cora picking him at the bar, feeling him up before declaring him 'perfect.' 

"Oh my God."

Derek grabs his wrist to stop him from getting off the bed. "That's not--" 

"Men!" Cora places a hand on Derek's chest, shoving him backwards so she can get Stiles onto his back again. She's not exactly gentle about it. "Men and their obsession with dick size! First of all, Derek's not _that_ big. And you are--"

"Perfect," Derek interjects. "Your dick is perfect." 

Stiles tilts his head in his best _bitch, please_ glare.

"You don't know, okay? You don't know what it's like." Derek shifts on the bed so his dick's trapped by the mattress, hidden. "You don't know how much I want--" His eyes trail down Stiles' body, lingering over his lips, his abs, the now soft cock nestled in a patch of dark hair. Stiles wants to cover himself, but Derek looks _hungry_ for just another second of being allowed to look. Stiles' small dick perks up at the attention.

"Can I--" Derek reaches out, but stops himself.

Stiles is nodding, he must be because his head's starting to feel dizzy and Derek's fingers close around his wilting erection. He pulls back after a couple strokes, licks his palm and wraps around the shaft again. His hands are huge and _hot_ and Stiles arches, eyes closed as he focuses on nothing but the tight heat surrounding him. In no time, he's hard again, pumping up into Derek's fist. The inky black insecurity from the moment before slips away.

"You're going to have to stop that if you don't want this over right now." 

"Sorry."

"S'okay, dude. You're welcome to jack me anytime. But I think you've got other plans."

Derek's cheeks go so red, and Stiles wants to reach out to touch and see how hot they are. "It's Cora's birthday," Derek says, like that explains everything going on tonight. Stiles nods; he's figuring it all out, at last.

"Condom?" Stiles says.

Cora and Derek exchange looks. There's some silent conversation going on between them until Derek nods, and Cora smiles and says, "You okay with bareback? I'm on the pill."

"And we're all virgins," Derek says.

"We are?" Stiles raises his eyebrow at Derek. 

"I wouldn't--" Derek shifts, uncomfortable under Stiles' stare. "Cora's been too young for--"

Cora rolls her eyes. "Fucked up rules. I told you."

She pulls Stiles on top of her and he braces his hands on either side of her head. His cock grazes her soft abs as she shifts up. 

"I'm … yeah." Stiles squeezes his eyes closed trying to remember why this is so important. "I swore I'd never. I mean. The lectures my dad --" 

"We're clean. Both of us. We've never touched anyone but each other. And you."

"Oh God," Stiles mutters, already knowing he's lost. He meets her for a sloppy kiss, moaning as she rocks her body up into his again. "Yeah. First time here too. I'm clean."

It makes him nervous. But a hot twinge in his stomach says it a good nervous -- the kind of nervous that makes his blood pump and his dick harder. Stiles accepts he's just making bad decisions left and right tonight.

As he settles himself lower, his cock hovering between Cora's legs, the tip close enough to feel the hot dampness of her curls, he's not entirely sure this isn't a weird dream. If it is, he'll definitely wake from it with sticky sheets.

Sliding inside is easier than he thought it would be. He'd imagined himself missing or not fitting or getting a 'do you even know what you're doing?' -- some terrible porno gag reel worthy first time. Instead, Cora's positioned perfectly, slick and open, and his cock just slides in, slow and steady until he's buried inside her completely. 

He watches her close her eyes and exhale. "Yeah," she breaths. Her throat works through a few swallows. "It's good." She smiles, clamps down around him, and Stiles almost loses it right there.

"I'm not going to last," he sputters.

"Then move, idiot." 

"Yeah, okay." Stiles snaps his hips, moving off instinct now and not even trying for grace or style. The feeling of being inside her is hot and tight and wet; every clichéd thought about sex that ever was fills his thoughts. His brain has gone completely off line. He can't process anything at the moment but how to move his hips to _keep feeling like this_. His muscles strain as he moves faster, the slap of naked flesh filling the room.

"Yes." Cora scratches his back as she clings to him, a counterpoint to the almost unbearable pleasure as she tilts her hips up to meet each thrust. "Fuck, feels good."

Stiles' eyes catch Derek's then, looking for the approval that he didn't even realize he wanted so badly. 

Derek's spread out beside them, naked, one hand stroking his monster cock. In the shadowy light of the bedroom he looks like artistic porn, rumpled sheets and a nude Adonis. Stiles wonders if he has any idea just how gorgeous he is or if he thinks no one would see past his dick size. It's enough of a downer that Stiles earns himself a few more minutes before he shoots off. 

He pushes up onto his knees, slipping out for just a moment before pulling Cora close again, her ass lifted a bit to sit on his thighs. Her legs spread wide and the sight's beautiful. He understands for the first time why people would take pictures of themselves having sex; he wants to remember this forever. When he slips back in, the angle's completely different and they both let out a gasp. 

"Okay?" he asks and Cora nods.

The best part of the new position is that it lets her get a hand down to play with her clit. He watches for a moment, mesmerized. It's so fucking hot. His dick can feel the vibration of her rubbing herself off, and Stiles moans, starts again with a jerky fast rhythm, chasing the inevitable.

He pants, straining to hold himself back. "Gonna --"

Cora's heels dig into the bed, her back arching off the mattress to present a perfectly positioned hole for him to fuck into for the last desperate threads of his control. "Do it." 

He slams hard into her, over and over, until she's scrambling to hold the headboard and avoid knocking into it. Stiles' orgasm crashes over him, sharp and bright, as he buries himself deep and just holds. He grips her waist, every muscle straining with his release, until the intensity fades and he's left a trembling sweaty mess.

He's wrecked, still suffering through the tremors as he drags in a few harsh breaths. He had sex. And it was fucking awesome. He's still inside Cora, his fingers still clutching at her hips like it's the only thing keeping him upright. 

He's got his eyes pressed closed as he pumps his softening cock slowly in and out of her messy pussy. He never wants the moment to end.

The gentle pressure of warm lips on his snaps him out of his stupor, just enough for his eyes to flutter open. The drop closed again as Derek cups his jaw and the kiss deepens, all stubble and tongue. Stiles hums at the unexpected pleasure of kissing a man. They kiss until he's soft enough that his cock slips out. 

He grimaces at the unexpected cold air surrounding his wet dick.

They break the kiss and both turn Cora. She'd laid out, legs spread, fingering herself though the swollen, slick mess of her cunt. Derek's fingers soon join hers, playing gently, burying his knuckles until they're glistening with the dribbling come. He looks fascinated, maybe a bit jealous. 

Derek's cock, even hard, is actually kinda floppy, he realises, though he's big enough that that beast must take a hell of a lot of blood to get completely rigid.

Stiles can't help but look at the tender longing in Derek's eyes and wonder how long they've waited, how long Derek's been in a state of constantly holding back, never taking what he wants even though he's got a willing partner in his bed. How did it get to the point of actively encouraging the woman he obviously loves to go out and find someone else. 

"I've got an idea," Stiles says before he's even though it through. "Lie back," he tells Derek.

Tugging Cora to sitting, he whispers, "You willing to try something? Stop me if you're not."

"Of course I'll stop if I'm not." The look she gives him says how willing and capable she is of hurting him if he were to even try to force her into anything. 

"Right." Stiles looks nervously at Derek, who surprisingly laid himself on the bed without question. "Straddle him," he says to Cora.

"What --" Derek starts to sit up, but Cora's hands on his chest shove him back.

"Trust me," Stiles says. "You both want this, right?" What is his life that he's not just complicit in this incest, but actively _enabling_ it? 

"Yes," Cora says, straddling Derek without further debate. Derek's cock is trapped against his belly as she lowers herself so that his shaft slides easily against her slick cunt.

"Yes." Derek grunts, grabbing Cora's hips, helping her move back and forth along his cock. His eyes are wide, staring at her like he can't believe she's there. 

They're lost in each other, in the pleasure of the moment, and Stiles almost leaves them be, but he thinks, maybe, this can go further. 

"Can you lift up a bit?" Stiles asks, grabbing Cora's hips along side Derek's hands to help her understand his meaning. 

Cora's brow furrows at Stiles interrupting, but she sits up on her knees, her ass hovering above Derek's crotch. 

"Perfect." Stiles gets between Derek's legs, behind Cora, and lifts Derek's cock until the tip grazes Cora's entrance. 

Derek hisses. "No."

"Just the tip, Derek."

Cora nods, understanding. "I want this," she tells her brother, her hands stroking Derek's chest like she's calming a frightened cat. "You won't hurt me."

When Derek huffs, "You say stop, we stop," Stiles wraps two hands around Derek's cock. 

The shaft is already slippery from Cora's cunt grinding against it. He knows it's mostly covered in his own come, and it should be gross, but it's anything but. Instead he's pleased it eases the way as he strokes Derek's big dick a bit stiffer so he can use the head to play with Cora's wet curls. 

Cora leans back against Stiles' shoulder for balance. He wishes he had a free hand to play with her, but she seems pretty content with her own fingers working her clit.

With the sounds they're both making, Cora and Derek are fucking _loving it_ , just letting Stiles maneuver them as he wants, _playing with them_ like they're dolls. Derek's thrashing, tearing at the sheets as slowly, slowly, Stiles works the fat head into Cora's folds until it starts to sink inside. Cora just braces herself, keeping still, thighs trembling.

Then all at once it disappears and Cora claws at Derek's chest, crying out like she's out of control, delirious with her next orgasm. Her cunt is stretched so wide, red and glistening wet around Derek's thick shaft. She can't seem to keep still, like she's unsure if she wants it deeper or if she can even handle any more.

"Can't." Derek's hips are jittery as he fights the instinct to push up and in and just _take_ what he needs. Stiles whispers assurances and pumps him fast, hands wrapped tight around the still exposed shaft. His hands bump against Cora's cunt with each stroke, making her cry out, writhe with the pleasure of it. 

Derek goes tense, his thighs squeezing Stiles between them. "Can't," Derek gasps, and he's coming. The head of his cock stays buried in his sister, pumping his jizz inside. 

"Derek, Derek." Cora's rambling, rocking her hips so she slips down just a little more and inhales sharply. "God. You and your stupid beautiful dick." 

In the next second, she loses her ability to stay up and collapses onto Derek's chest. The flare of his softening dick's head slips free as she moves and Stiles watches the come dribble out, his and Derek's mixed together, making a sticky mess all over Derek's pubes. 

Derek kisses his sister and they start to roll around, giddy and laughing, like any couple that is young and in love,having just shared something precious. The moment's intimate, but too joyous for Stiles to feel uncomfortable witnessing it. He's sincerely happy for them, in a way that he could never imagine, had he ever fantasized about anything this bizarre. It takes him by surprise. 

"Holy shit," Stiles mutters.

"Agreed." Cora grins, lazy and tired, pulling Stiles to the bed.

Stiles watches Derek's wide-eyed, stunned face as his lips slowly make their way into a smile. It looks like the kind of smile that's taking up permanent residence, content and satisfied. He feels like he's somehow given Derek a gift, given them _both_ something special, led them down a path they hadn't been willing or able to walk down alone. He's not really sure when this night got so fucked up that he's landed here, but he can't regret a moment of it.

He's hard again, but he's too tired to care, the adrenaline crash and the fading alcohol making his eyes droop. He debates dressing for about ten seconds, then feels a sheet being pulled up and two hot, naked bodies press to either side of him. He doesn't feel like walking home smelling like sex at 3AM anyway.

 

He wakes to the smell of coffee and the feeling of a mouth on his dick. For a second he thinks maybe he was right about serial killers after all: this is definitely after-life worthy.

Stiles eyes snap open as the beautiful heat disappears and his wet dick is exposed to the air. He shivers at the loss. 

"Morning," Derek says, his lips close enough to graze the leaking tip of Stiles cock. 

Stiles grins stupidly as he blinks away his sleep. "Yeah, good morning. _Best_ morning." 

His face feels tacky and his mouth needs serious freshening; the memory of passing out without cleaning up last night suddenly makes him self-conscious. He wants to apologize for his dick. It's got to still taste like spunk and Cora -- only Derek's swallows him down again, humming in pleasure and Stiles realizes that might be Derek's favourite flavor of dick. 

Maybe that should freak him out or disgust him. But the harsh light of day doesn't seem to illuminate Stiles' morals any more than the alcohol fog did last night. Mid-blow job is no time to examine his ethics anyway. 

Certainly not with the waves of pleasure that mouth is giving him. Fuck. He'd heard blowjobs were amazing. He'd imagined just how amazing nearly every night as he stripped his cock raw with his own hand and spit for lube. But nothing prepared him for the intensity of _this_. 

Derek's tongue is hot and wet, sliding against the underside of his cock like he's tracing the vain. Stiles whimpers, scrambling for something to ground him because it feels like he's falling, off balance and maybe losing his mind. 

Helpless, Stiles focuses on watching Derek work his cock, the off-rhythm bob of his head, the play of muscles of his naked back. A tattoo, identical but maybe three times the size of his sister's, dances across his back with each movement. Stiles tries to memorize every detail while his brain melts.

Derek's mouth is made for cock. He's opening his throat like a pro, swallowing him down, burying his nose in Stiles' pubes like he can't get enough of Stiles' scent. It's too much. Stiles almost loses it.

His hips jerk up, out of control.

The moment's lost instantly. Derek gags and has to pull off, choking. His eyes are watering and Stiles feels like an utter shit.

"Sorry." Stiles rushes to get the words out, petting Derek's hair, his face. "Oh God, I'm so sorry. I never-- never had anyone--"

Derek shakes his head, rubbing his throat. "First time here too."

You don't have a brother? Stiles _almost_ says, but he's too concerned about kissing Derek, not caring about the nasty taste of either of their mouths. Stiles' "I'll be careful" tumbles over Derek's "I'll try again." 

Stiles lies back, still stroking Derek's hair. "Go slow," he says as Derek wraps his lips around Stiles' cock once again. He doesn't go slow.

It never takes long to handle his morning wood even with just his own hand, and Derek's bold, brave attempt to deep throat is going to get Stiles off even faster, no matter how Stiles fights to make it last.

"Derek," he gasps, squeezing his thighs to try to stop thrusting up into the scratch of stubble and smooth, wet heat. It's impossible. His balls are already stirring, body tensing with anticipation. "Derek," he repeats, this time like a warning as he tugs on Derek's hair to get him to pull off.

Derek makes it just in time to miss getting a dripping beard. Stiles, orgasm-drunk, watches the spurts of come spatter his groin, fascinated as his dick twitches and pumps out the last of his come. It's different, kind of amazing, watching without touching, watching with an audience just a riveted as he is. 

Kneeling at his side, Derek stares at him hungrily, like he's never seen a dick. Cora's in a towel, watching from the doorway. Her face is pink from the shower, mouth slack from the show she just caught the end of. Stiles' cock jerks under the scrutiny, trying defiantly to stay hard. 

"I want to keep him," Cora blurts out.

Derek snorts, falling back to the bed, curling up to Stiles. "He's not a dog." His arm falls possessively over Stiles' stomach.

Cora rolls her eyes, dropping her towel and joining them. Her skin is warm and she smells so shower-clean that Stiles nuzzles into her damp hair. They must be ripe in comparison but she doesn't seem to mind. 

Stiles closes his eyes. He needs to shower, badly. He's got groceries to get and homework to do. But not quite yet. He wants this to last as long as they're willing to let him stay. 

"You should still keep him," Stiles mumbles, otherwise pretending to have fallen asleep again. 

Stiles can feel the muscle movement against his chest as Derek shrugs. 

"Okay," Derek says, like he's willing to give Cora anything she wants, but Stiles feels Derek's arms curl around him just as tight as Cora's.

**Author's Note:**

> You can find me on tumblr at [marguerite26](https://www.tumblr.com/blog/marguerite26)


End file.
